Transcript 01501_ch04 - CarlPetersheim.us

JavaScript, Fourth Edition
Chapter 4
Manipulating the Browser Object Model
Objectives
• Study the browser object model
• Work with the Window object
• Study the History, Location, and
Navigator objects
• Use JavaScript to refer to windows and frames
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Understanding the Browser Object
Model
• Browser object model (BOM) or client-side
object model
– Hierarchy of objects
– Each provides programmatic access
• To a different aspect of the Web browser window
or the Web page
• Window object
– Represents a Web browser window or an
individual frame within a window
– Called the global object because all other
objects in the browser object model are
contained within it
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Understanding the Browser Object
Model (continued)
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Understanding the Browser Object
Model (continued)
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The Document Object
• Document object
– Represents the Web page displayed in a
browser
– Has methods such as
• write() and writeln()
– Contains all elements on a Web page
• Including forms created with the <form> element
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Referencing JavaScript Objects
• Some of the objects in the browser object
model represent arrays
– Such as frame[], forms[], or images[]
• To refer to a JavaScript object in code
– You must refer to all of the objects that contain
it, with the object names, separated by periods
• Example: Pine Knoll Properties Web site
– Six prewritten Web pages:
PineKnollProperties.html, colonial.html,
contemporary.html, cottage.html, ranch.html,
and townhouse.html
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Referencing JavaScript Objects
(continued)
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The Window Object
• Window object
– Includes several properties that contain
information about the Web browser window
– Contains methods that allow you to manipulate
the Web browser window itself
• self property
– Refers to the current Window object
– Using the self property is identical to using the
window property to refer to the Window object
• Web browser assumes you are referring to the
global object
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The Window Object (continued)
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The Window Object (continued)
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Windows and Events
• The click and dblclick Events
– The click event is often used for anchor element
– Web browser handles execution of the onclick
event handler automatically
– You can override an anchor element’s automatic
onclick event handler
• Add to the <a> element an onclick event handler
that executes custom code
– The dblclick event works like the click event
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Windows and Events (continued)
• The mouseover and mouseout Events
– Use the mouseover and mouseout events to
create rollover effects
– Rollover is an effect that occurs when your
mouse moves over an element
– mouseover event occurs when the mouse
passes over an element
– mouseout event occurs when the mouse moves
off an element
– One common use is to change the text that
appears in a Web browser status bar
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Windows and Events (continued)
• defaultStatus property
– Specifies the default text that appears in the
status bar whenever the mouse is not positioned
over a link
• Example: Pine Knoll Properties Web site
– Add the defaultStatus property
• Common use of rollovers is to replace (or
swap) an image on a Web page
• The mousedown and mouseup events
– mousedown event occurs when you point to an
element and hold the mouse button down
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JavaScript, Fourth Edition
Windows and Events (continued)
• The mousedown and mouseup events
(continued)
– mouseup event occurs when you release the
mouse button
• Example: Pine Knoll Properties Web site
– Modify the <img> element in the
PineKnollProperties.html document
• So the second image in the banner displays when
you hold the mouse over it
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Opening and Closing Windows
• When a new Web browser window is opened
– A new Window object is created to represent the
new window
• Be familiar with how to open a link in a new
window by using the <a> element’s target attribute
• Example: Pine Knoll Properties Web site
– Open links in new windows
• Opening a Window
– open() method of the Window object
• Opens new windows in the strict DTD
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Opening and Closing Windows
(continued)
• Opening a Window (continued)
– Syntax
window.open(url, name, options, replace);
– You can customize its appearance using the
options argument
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Opening and Closing Windows
(continued)
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Opening and Closing Windows
(continued)
• Opening a Window (continued)
– Example: Pine Knoll Properties Web page
• Links use the window.open() method instead
of the target attribute to open the URLs in a
separate page
– A Window object’s name property can be used
only to specify a target window with a link
• And cannot be used in JavaScript code
– Assign created window to a variable
• If you want to control it
– focus() method
• Makes a window the active window
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Opening and Closing Windows
(continued)
• Opening a Window (continued)
– Example: Pine Knoll Properties Web page
• Add a focus() method to showProperty()
• Closing a Window
– close() method
• Closes a Web browser window
– window.close() or self.close()
• Closes the current window
– Example: Pine Knoll Properties Web page
• Add links to each of the property Web pages that call
the close() method
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Working with Timeouts and Intervals
• Window object’s timeout and interval methods
– Creates code that executes automatically
• setTimeout() method
– Executes code after a specific amount of time
– Executes only once
– Syntax
var variable = setTimeout("code",
milliseconds);
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Working with Timeouts and Intervals
(continued)
• clearTimeout() method
– Cancel a setTimeout() before its code
executes
• setInterval() method
– Repeatedly executes the same code after being
called only once
• clearInterval() method
– Used to clear a setInterval() method call
• Interval methods are most often used for
starting animation code
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Working with Timeouts and Intervals
(continued)
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The History Object
• History object
– Maintains an internal list (history list) of all
documents that were opened during current Web
browser session
• Security features
– Object will not actually display the URLs contained
in the history list
– In Internet Explorer this is only possible if the
currently displayed Web page exists
• In same domain as Web page containing JavaScript
code
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The History Object (continued)
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The Location Object
• Location object
– Allows you to change to a new Web page from
within JavaScript code
• Properties of the Location object allow you to
modify individual portions of a URL
– Web browser automatically attempts to open
that new URL
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The Location Object (continued)
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The Navigator Object
• Navigator object
– To obtain information about the current Web
browser
– Can determine which type of Web browser is
running
• with statement
– Eliminates need to retype the name of an object
• When properties of the same object are being
referenced in a series
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The Navigator Object (continued)
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The Screen Object
• Screen object
– Obtains information about the display screen’s
size, resolution, and color depth
• Common use of the Screen object properties
– To center a Web browser window in the middle
of the display area
• Example: Pine Knoll Properties Web page
– Property window is centered in display area
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The Screen Object (continued)
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Referring to Frames and Windows
• Learn how to refer to frames and windows from
within Web pages
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Using the target and base Attributes
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Using the target and base Attributes
(continued)
• target attribute
– Determines in which frame or Web browser
window a document opens
• Based on the value assigned to an <a> element’s
target attribute
• Or the value assigned to a <frame> element’s
name attribute
• Example: Pine Knoll Property Web page
– Work on a prewritten, frame-based version
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Using the target and base Attributes
(continued)
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Using the target and base Attributes
(continued)
• <base> element
– Used with the target attribute
– Specifies a default target for all links in a
document, using the assigned name of a
window or frame
• You must use the transitional DTD
• Example: Pine Knoll Properties Web page
– Modify the PropertiesList.html document so it
includes a <base> element instead of multiple
target attributes
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The parent Property
• frames[] array contains all frames in a
window
• parent property of the Window object
– Refers to a frame within the same frameset
• Combined with the frame’s index number
• With nested frames
– Use the parent property and the name you
assigned to a frame with the <frame> element
– Nested frames are assigned to the frames[]
array in the order in which they are encountered
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The parent Property (continued)
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The parent Property (continued)
• Example: Pine Knoll Properties Web page
– Modify the PropertiesList.html document so the
links open in the right frame
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The top Property
• top property
– Refers to the topmost window on a Web page
• When working with frames, the top property
refers to the window that constructed the
frames
• Example: Pine Knoll Properties Web page
– Modify the PropertiesList.html document so the
links are opened using the top property instead
of the parent property
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Summary
• Browser object model (BOM) or client-side
object model is a hierarchy of objects
• Top-level object in the browser object model is
the Window object
• To refer to a JavaScript object in code, you
must refer to all of the objects that contain it
• Document object is arguably most important
object
• History object maintains a history list of all
the documents that have been opened
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Summary (continued)
• Location object allows you to change to a
new Web page from within JavaScript code
• Navigator object obtains information about
the current Web browser
• with statement eliminates the need to retype
the name of an object
• Screen object obtains information about the
display screen’s size, resolution, and color
depth
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Summary (continued)
• target attribute determines in which frame or
Web browser window a document opens
• Use the target attribute with the <base>
element to specify a default target for all links
• To refer to a frame within the same frameset,
use the parent property
• top property refers to the topmost window on a
Web page
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